The present invention relates to a constant current circuit and an oscillating circuit controlled by the constant current circuit, the oscillating circuit capable of being used as a variable-frequency clock generator in a battery-powered computer.
Various methods for saving electric power are implemented in a computer which is powered by a battery. For example, operating voltage thereof is set lower in such operation modes not requiring high speed as the mode selection prior to the arithmetic processing, together with lowering the frequency of clock signal. Lower operating voltage and lower clock signal frequency both result in the reduction of power consumption.
In conventional battery-powered computers, one of the following techniques is applied thereto for changing clock signal frequency as described above: the first is implementing plural oscillators for generating clock signals of different frequencies, and selecting respective one of the oscillators, when performing, for example, a high speed operation such as arithmetic processing or a low speed operation such as mode selection; the second is providing a single oscillator of a relatively high frequency, and obtaining a desired low frequency by demultiplying the high frequency. However, these techniques include drawbacks of increase in the hardware such as oscillators and selecting circuits, and, of increase in the cost of the computers. Another drawback included in the above conventional technique is such that the lower frequency can not be changed continuously.